Rotational symmetry breaking in the superconducting state of doped bismuth selenides

Topological superconductors (TSC) have been attracting huge interest due to their potential applications to topological quantum computation. Particularly, theories predicted that superconducting doped Bi₂Se₃ is a TSC and shows a nematic order in the TSC state. Recently, Cu, Nb and Sr-doped Bi₂Se₃ have shown the rotational symmetry breaking by means of NMR, heat capacity, torque magnetometry and transport H_c2. We probed the rotational symmetry of doped Bi₂Se₃ samples in both normal and superconducting states by torque magnetometry. The magnetic field was applied in-plane and the symmetry of magnetic anisotropic susceptibility as well as hysteresis loop was measured. We observed that the superconducting hysteresis loop, as well as the anisotropic magnetic susceptibility, was enhanced along one direction, indicating the rotational symmetry breaking. The relationship between the TSC state and rotational symmetry breaking will be discussed.

T. Asaba et al. Physical Review X7.1 (2017): 011009.